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Lars Lund

05 Apr 2024 07:41

How to Grow Olives

It's not only in Spain and Italy that you can grow olives. 

By Lars Lund

If you've bought an olive tree, you're in for a treat. It's one of those wonderful plants for your greenhouse and contributes to making your greenhouse a bit exotic, even somewhat sacred. In ancient times, olive trees in temples were considered holy trees.

Originally, the olive tree comes from the Orient. Later, it spread to the Mediterranean countries.

With climate change, the olive tree might spread further north.

Both in literature and on the internet, you will read that olives do not tolerate frost and therefore must be protected during the winter. However, the fact is that olives do quite well throughout the year in my own greenhouse, in the open air, and in several English gardens. The prerequisite for having it in the greenhouse and, not least, in the garden, however, is that the olive must be planted directly in the ground. It's the roots that cannot tolerate frost, while both the stem and leaves can withstand frost, although it should not be for too long without protection. Minus ten degrees Celsius in shelter is generally not a problem. 

How to Care for Your Olive in Summer and Winter

Having an olive in your garden or greenhouse is a great choice if you want something exotic in your garden. You can even get fruits, which you can harvest and eat after preparation. In their natural growing areas, an olive tree can grow up to twenty meters and live for several thousand years. Here, they will be smaller, but you can buy large imported trees. The tree grows very slowly, so if you buy a plant half a meter tall, you should expect it not to grow much taller than two meters with you. In other words, it's a small tree and fortunately also an easy tree to care for.

Acquiring an Olive Tree

As is the case with so many plants, there are different varieties of olives. In Italy alone, there are over 3,000 different kinds. All olive fruits are green to start with and change color as they mature. When they are dark brown, most growers harvest their olives because they yield the best. However, they do not produce as good oil when they are brown as when they are green. Therefore, olive oil harvested from green olives is more expensive.

Tip

Often, it's Spanish or Italian olive trees that are sold in England. Experiences here among garden owners suggest that it's advantageous to buy a tree from Italy. Here, the winters are a bit longer, and therefore the varieties from there fit well with English conditions. However, some have bought from Spain and also had success with them. Here it's mainly about larger trees.

Tip

Another tip I got from an olive tree seller is to buy a tree that already has olives set on it. It can take from 7 up to 15 years before the tree bears olives, and it seems that the trees that bear olives will continue to do so, while trees you buy without any olive buds may never produce fruit or only produce very few fruits. Some are not self-pollinating but must have a pollinator from another tree.

Sowing Olives

You can also try to sow olives and create your own plant. It should just not be from a stone from the pickled salted olive. Here, the fruit setting is often destroyed by the brine. Scrape the fruit flesh away from the core. Soak the core in lukewarm water (change the water now and then) for a day. Use coarse sandpaper and polish the core, this makes germination quicker. Place the core with the tip upward in some sowing soil and cover it with about 1 cm of soil. Place the pot in a warm and bright spot. 20-25 degrees Celsius is perfect.

Cuttings

Propagation of olive trees is done professionally by grafting, but you can successfully use semi-ripe cuttings. Take the cuttings from May to September. Remove leaves from the bottom 2-3 cm of the stem.

Tip

A tip is to dip the end in cinnamon. It prevents fungus. Stick the cutting in moist sowing soil and cover with plastic or place them in a germination box. Room temperature is warm enough.

Soil

If your olive will be in a permanent bed in your greenhouse or out in your garden, ordinary garden soil is excellent. However, you should very much like to mix sand and gravel into the soil, so the soil isn't too heavy. Olives love water, but the roots must not stand in water for too long. It's possible to buy a so-called Mediterranean soil and if so, buy one without sphagnum. Do not plant deeper than the depth the tree was in the pot. The stem can rot if it stands in moisture.

Planting in Bed

Let the root ball soak water for 12 hours. Dig a hole that is bigger than the root ball and also fill the hole up with water. When the water has sunk, you can plant the root ball and fill soil on. It's a good idea to give the tree's leaves a shower. In winter, the soil should be covered with insulating material.

Planting in Pots

Choose a pot that is larger than the one you bought the plant in. Olive trees do not like too much replanting, so it needs space to grow. If you choose a pot with as large a bottom as possible, it stands much more stable than a pot with a small bottom. The pot should be unglazed, so the roots can breathe.

In a pot, there may well be a bit of clay to hold on to the water. Pots dry out faster. Mediterranean soil contains washed gravel, clay, and iron-rich lava, and the soil's pH is adjusted, so plants more easily absorb iron. In winter, the pot should be placed somewhere as frost-free as possible, and the pot wrapped in insulating material.

 

Care

Care of Pot Plants

In the summer, an olive likes to have water, and although it's not optimal, it can tolerate being watered little but prefers to have a good soaking once a week. On the other hand, it can tolerate drying out between waterings. The thirst is greatest at the end of spring and over the summer. Here, depending on the weather, you may need to water twice a week. If it's very windy or hot, the water need is greater than in calm overcast weather. Stick a finger in the soil and feel if the soil is moist. If you're not into dirty nails, you can buy a moisture meter for a very small amount.

Watering gradually decreases towards autumn. The warmer the plant stands, the more water and light it needs. This means if you take it inside the house in winter, you should count on artificial light in the dark time and keep an extra good eye on the watering. A rule of thumb says that when the plant is in a heated room at around 20 degrees Celsius, it should be watered. If it's at 15-10 degrees, it should be watered once a month, and under ten degrees only if it loses leaves otherwise not. It preferably should have a cool period to set fruit buds.

Fertilize only in the summer. Olive fans choose long-lasting Osmocote Mediterranean fertilizer, where it's fertilized twice a year: spring and autumn. Others choose a liquid fertilizer, where it's watered every other week. 

Plants in the Garden, Winter

Here, watering ends in mid-October. If it rains a lot, it's a good idea to protect against too much water. Fertilizer for plants dug down in the garden is not necessary, but compost is always good. At day frost below –7-10 degrees Celsius, you can protect the crown with a fleece fabric. Either as pre-shaped bags that can be bought or with fabric in rolls. Fleece fabric in rolls is cheaper, and you can shape it around the tree yourself. The stem does not need to be wrapped.

Pruning

It's rarely necessary to prune a smaller tree, but the tree can certainly tolerate pruning. It promotes growth. Most of the pruning is about shaping your tree as you want it and cutting away sick and dead branches.

Diseases and Damages

Leaf Fall

Olives can get yellow leaves, which can be a sign of overwatering. If the green leaves fall off, it's a sign of the opposite.

Brown spots on leaves, especially the tips, can be due to over-fertilization, too much water, or problems with the fertilizer composition.

Mealybugs occasionally appear and are not so bothersome for olive trees themselves, but they cause damage to the bark since they live off sap. It can leave your tree open to infection and frost damage. Fortunately, it's easy to treat mealybugs. It's just to wash the bark with a mixture of dish soap and water. The treatment should remove the problem without much trouble. There are also several chemical treatments for mealybugs.

Phytophora Root Rot

Caused by poor drainage or a bad root system that causes the root to rot.

Peacock disease is a disease that starts with circular spots on the leaves. It can be in the form of soot spots. Gradually, the spots are surrounded by pale yellow tissue. The disease spreads to other leaves, and the leaves fall off. It's a fungal disease and should therefore be treated with a fungicide that is sprayed on in the morning. The best is to prevent with a spraying in November and again in February.

Tip

Your own pickled olives

Wash olives in cold water. Put the fruits in a pot or a roasting pan. Cover with salt, lemon peel, and herbs. Set them cold for ten days. Turn them once a day. After ten days, wash them clean of salt. Dry them on the roasting pan in an oven at 785 degrees for a couple of hours. Fill them into sterile jars. Pour virgin oil over, a little dried chili, garlic cloves, and herbs to taste.

Om Lars Lund

Lars Lund
Danish horticulturist and journalist
Lars Lund has for many years engaged in the garden and greenhouse. Lars has published many books about greenhouses, and he has participated in many Danish horticultural TV shows. He is a walking garden encyclopaedia, and he has answers for most basic cultivation questions – also the more ambitious ones.  

Get to know Lars Lund